1. Field of the Invention
The present invention relates to an ink jet recording device, and more particularly to an ink jet recording device having a capability of detecting the life of an ink jet recording head.
2. Description of the Related Art
In a conventional ink jet recording device such as a thermal ink jet recording device designed to rapidly heat ink by a resistance heater provided in an ink jet recording head and thereby generate bubbles in the ink, a pressure of which functions to jet ink droplets from nozzles, the ink jet recording head is subjected to a stress due to heat, pressure or chemical reaction with the ink during the operation for a certain period of time. The stress causes an increase in resistance of the heater or rapid heating of the heater to scorch the ink. As a result, a jet quantity of the ink is decreased and a normal jetting operation cannot be achieved to remarkably reduce an image quality.
In Japanese Patent Laid-open Publication No. 61-55867, the abnormal condition of the heater is detected by providing means for detecting a current leaked from the heater through the ink, thereby detecting the life of the ink jet recording head from the current value detected by the detecting means.
However, in such a conventional life detecting method as described in Japanese Patent Laid-open Publication No. 61-255867, special work of making electrodes for leakage current detection at an ink jetting portion is necessary to cause an increase in cost. Further, so long as any abnormality of the heater does not occur, the life of the ink jet recording head cannot be detected. Thus, the expiration of the life of the ink jet recording head cannot be predicted.
In an integral type ink jet cartridge constructed integrally of an ink jet recording head and an ink tank, a residual ink detecting device for detecting a quantity of ink remaining in the ink tank is described in Japanese Patent Laid-open Publication No. 3-247456. The residual ink detecting device is designed to detect a residual quantity of ink having reached a predetermined value or less from a change in resistance between electrodes and then count the number of print scans or the number of printed sheets, thereby detecting an ink consumption. When the residual quantity of ink thus defined from the detected ink consumption becomes the predetermined value or less, the use of the ink jet cartridge is stopped to avoid a reduction in print quality.
In such an integral type ink jet cartridge including the ink jet recording head and the ink tank integral with each other, the ink tank cannot be removed from the ink jet recording head, so that when the ink contained in the ink tank is fully consumed, the life of the ink jet recording head expires. In other words, the detection of a residual quantity of the ink in the ink tank in such an integral type ink jet cartridge means the detection of the life of the ink jet cartridge.
However, the technique described in Japanese Patent Laid-open Publication No. 3-247456 has a problem similar to that of the technique described in Japanese Patent Laid-open Publication No. 61-255867. Further, the technique described in Japanese Patent Laid-open Publication No. 3-247456 is originally intended to prevent a reduction in print quality due to a decrease in residual quantity of ink, and it is not a technique of detecting the life of the ink jet recording head. In addition, the technique described in Japanese Patent Laid-open Publication No. 3-247456 is incapable of detecting the life of an ink jet recording head of a disassemblable type ink jet cartridge including the ink jet recording head and an ink tank removably mounted thereto.
It is considered that the method of detecting an ink consumption by merely counting the number of print scans or the number of printed sheets as described in Japanese Patent Laid-open Publication No. 3-247456 may be applied to the detection of the life of the ink jet recording head. That is, the number of operations of each nozzle per print scan or printed sheet is preliminarily expected and the number of serviceable operations of each nozzle is preliminarily defined. Then, the number of print scans or the number of printed sheets is counted to thereby detect the number of actual operations of each nozzle. When the number of actual operations detected above approaches the number of serviceable operations, it is determined that the life of the ink jet recording head has nearly expired.
However, in an ink jet recording device employing various kinds of printing paper having different sizes, the number of print dots of each nozzle (i.e., the number of operations of each nozzle) per print scan or printed sheet varies according to the difference in size of the printing paper, causing an increase in detection error of the life of the ink jet recording head.